The present invention relates to (a) a brake shoe for disc brakes having a retaining spring which is fixed to the pad back plate and is locked to prevent rotation thereof, and (b) a process for manufacturing such a brake shoe.
DE-OS 3842428 discloses a brake shoe of the afore-described type which is intended for use with a floating caliper spot-type disc brake. When assembled, the brake shoe, with its pad back plate, is in abutment with a brake piston of a hydraulic actuator. During braking, the brake piston acts directly upon the brake shoe, thereby forcing it against the brake disc. After the braking operation, the brake piston, in known manner, is withdrawn, by means of a roll-back sealing ring, a short distance opposite the actuating direction in order to set a clearance between the friction face of the brake shoe and the brake disc. To insure that the brake shoe follows that movement, it is clamped on the brake piston by means of a retaining spring. The retaining spring comprises three tongues which engage the hollow brake piston. One of the tongues, at the same time, serves to prestress the brake shoe vis-a-vis the brake housing to prevent the brake shoe from clattering in its guides, with the brake shoe being radially forced toward the brake disc axis. To safeguard this function, the retaining spring is fixed to the pad back plate in a predetermined position and is prevented from rotating during operation.
In the conventional brake pad, the retaining spring, in simple manner, is fixed by a single bolt or pin forced into the pad back plate. To prevent the retainer spring from rotating about the bolt, provision has been made for connecting the retaining spring, in form-locking manner, with a damping sheet which also is fixed to the pad back plate. However, this way of locking against rotation is not suitable for use with brake shoes not provided with a damping sheet.
Another means of fixation for locking against rotation of the retaining spring is disclosed by EP 0112255 B1 in which the pad back plate is provided with a molded, punched-through projection, having a D-shaped cross-section, protruding beyond the plate plane. The retaining spring is provided with a D-shaped hole for passage of the punched-through projection, with the form-locking connection preventing rotation of the retaining spring about the single point of fixation from occurring. The fixation is by riveting of the punched-through projection, for example, by wobble riveting.
However, this type of fixation has the disadvantage that strong forces are required for caulking or wobbling to deform the required material volume. In view of unavoidable manufacturing tolerances, the retaining spring, as such, or the pad back plate are likely to be bent so that the proper function of the brake shoe no longer is safeguarded.